High Northern Latitude Carbon Balance Over the 21st Century

It has been hypothesized that if or when the frozen soils of earth's Northern High Latitudes (NHLs, land poleward of 60°N) begin to thaw in response to any new spate of global warming that might occur, the metabolism of soil microbes will be enhanced and the decomposition of soil organic matter will accelerate; and it has been further postulated that this, in turn, will lead to an increase in soil organic carbon release to the atmosphere that will amplify global warming. Satellite and phenology studies, on the other hand, have shown that during the past several decades the planet's boreal forests have experienced greening and an increase in photosynthetic activity, which obviously extracts carbon (in the form of CO₂) from the atmosphere. In order to get some indication as to which of these two outcomes might likely predominate over the course of the 21st century, Qian et al. explored the potential magnitudes of the two sets of competing processes by analyzing the outputs of ten different models that took part in the Coupled Carbon Cycle Climate Model Intercomparison Project (C4MIP) of the International Geosphere-Biosphere Program and the World Climate Research Program, all of which models, in their words, "used the same anthropogenic fossil fuel emissions from Marland et al. (2005) from the beginning of the industrial period until 2000 and the IPCC SRES A2 scenario for the 2000-2100 period."

According to the authors, the ten C4MIP models predicted a mean warming of 5.6°C from 1901 to 2100 in the NHL; and the three researchers state that "the NHL will be a carbon sink of 0.3 ± 0.3 PgCyr^-1 by 2100." They also state that "the cumulative land organic carbon storage is modeled to increase by 38 ± 20 PgC over 1901 levels, of which 17 ± 8 PgC comes from vegetation [a 43% increase] and 21 ± 16 PgC from the soil [an 8% increase]," noting that "both CO₂ fertilization and warming enhance vegetation growth in the NHL." Thus, over the course of the current century, even the severe warming predicted by current climate models would likely not be a detriment to plant growth and productivity in the NHL. In fact, it would likely be a benefit, enhancing plant growth and soil organic carbon storage, which (in addition to their own virtues) would provide a significant negative feedback to global warming.

Additional Reference
Marland, G., Boden, T.A. and Andres, R.J. 2005. Global, regional, and national CO₂ emissions. In: Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, USA. Available at http://cdiac.ornl.gov/trends/emis/overview.html.